Pharmaceutical composition based on idazoxan, salts, hydrates or polymorphs thereof

ABSTRACT

A pharmaceutical composition comprising idazoxan or derivatives and their therapeutically acceptable salts, racemates, optically active isomers and polymorphs.

The present application is a continuation-in-part of copending U.S.application Ser. No. 10/974,675 filed Oct. 28, 2004, which claimspriority on French Patent Application No. 0312626 filed Oct. 28, 2003.Each application is hereby incorporated by reference.

The present invention relates to the pharmaceutical industry andconcerns the pharmaceutical dosage formulation of active principle. Moreparticularly, the invention relates to a stable formulation, suited toindustrial production, of non-film-coated tablets of idazoxan saltcomprising a dose of active principle of between 5 and 100 mg and havinga conventional release. These tablets are provided in a packaging whichis leaktight to water vapour. Preferably, the idazoxan salt used is anidazoxan hydrochloride polymorph.

Idazoxan is known for its antagonist properties with regard toα₂-adrenergic receptors. This compound is disclosed in Patent EP 033 655by its chemical structure, its process of synthesis, certainpharmaceutical formulations and its therapeutic application asantidepressant medicament. Idazoxan has been studied in human clinicalmedicine in the treatment of depression at doses varying between 5 and40 mg, three times a day, over four weeks and showed a significantimprovement on the Hamilton scale against placebo (Drug of the Future,10, No. 9, 782, 1985). Various studies have also been carried out onmonkeys or rats to evaluate the effects of the various compounds onsymptoms analogous to those of Parkinson's disease, such as the symptomsinduced by reserpine in the rat (F. C. Colpaert, Neuropharmacologie, 26,1431, 1987) or by the neurotoxin MPTP (F. C. Colpaert et al., Brain.Res. Bul., 26, 627, 1991). More specifically, Patent FR 92/14694 relatesto the use of idazoxan and of its derivatives in the preparation of amedicament intended for the treatment of Parkinson's disease, itsprogression in its idiopathic form and its evolution. Patent ApplicationFR 96/03674 relates to products comprising milnacipran and idazoxan ascombined pharmaceutical preparation for a simultaneous, separate orsequential use in treating depression and its various forms, andpathologies in which antidepressants are used.

Several problems have to be solved before envisaging the large-scaleindustrial use of idazoxan. In particular, it is necessary to find anexcipient compatible with this active principle, to select a form ofvehicle suitable for guaranteeing its stability and to look for amanufacturing process, taking into account in particular the problem ofhygroscopicity of idazoxan and its stability. Furthermore, the activeprinciple has to exhibit suitable physical properties in terms ofparticle size and of tabletability. It is therefore necessary to choosea suitable leaktight packaging which protects the active principle frommoisture. These are the problems, still unsolved, which the presentinvention intends to solve.

The present invention relates to a pharmaceutical composition comprising5 to 25% of a salt or of hydrate of idazoxan or of its derivatives, 10to 40% of micro-crystalline cellulose, 0.1 to 5% of lubricant, and from0.1 to 0.5% of colloidal silica and from 25 to 90% of lactose, withrespect to the total mass. Preferably, the present invention relates toa pharmaceutical composition comprising 5 to 20% of an idazoxan salt orof idazoxan hydrate, 10 to 40% of microcrystalline cellulose, 1 to 5% oflubricant, 0.1 to 0.5% of colloidal silica and from 29.5% to 84.8% oflactose, with respect to the total mass.

The term “idazoxan and its derivatives” is understood to mean thecompound of general formula I:

in which R represents a hydrogen atom, a linear or branched C₁-C₄ alkylradical and a linear or branched C₁-C₄ alkoxy radical, and itstherapeutically acceptable salts, its racemate, its optically activeisomers, and its polymorphs. Preferably, R represents a hydrogen atom, amethoxy radical or an n-propyl radical. One aspect of the presentinvention thus relates to a stable formulation, as defined above,comprising idazoxan of formula II:

Idazoxan hydrochloride has a proton at the C₂ chiral centre, with theresult that two potential R(−) and S(+) enantiomers exist. Thepharmaceutical composition according to the invention preferablycomprises the racemic mixture but it is possible to envisage theidazoxan of the composition being enriched in one or other of theenantiomers, indeed even comprising virtually exclusively one or otherof the enantiomers, given that it is possible to separate the twostereoisomers by means, for example, of a chiral column. The twoenantiomers have different pharmacokinetic characteristics (see Example8) but, even if the two enantiomers are separated, there exists aninterconversion from one form to the other both in vitro (underphysiological conditions, pH 7.4, 37° C.; see Example 8.1) and in vivo(see Example 8.2).

Polymorphic forms of idazoxan are also included in said definition.

In a preferred embodiment, the idazoxan salt is idazoxan hydrochlorideand the lubricant is glyceryl behenate, magnesium stearate beingincompatible with the active principle.

The pharmaceutical composition according to the invention isparticularly suited to industrial production and is stable. Aformulation is described as “able to be produced industrially” or“suited to industrial production” when the formulation makes it possibleto obtain batches on a rotary production device while satisfying themain tests of the European Pharmacopoeia as regards tablets. The term“stable” is understood to mean packaged tablets which generate less than1.5% of decomposition impurity after one month at 40° C., 75% RH(Relative Humidity), and at most 2% of impurity after 2 years at 25° C.,60% RH.

In an even more preferred embodiment, the idazoxan salt is chosen fromthe polymorphs of form I, II, III, IV, V and VI or a mixture of at leasttwo, of at least three, of at least 4, 5 or 6 idazoxan polymorphs. Thepharmaceutical composition is not intended to be limited to thepolymorphs of idazoxan or to a mixture of polymorphs of idazoxan. Otheridazoxan-based compounds suited to use in this pharmaceuticalcomposition are presented in U.S. Pat. Nos. 2,979,511 and 4,818,764.

The polymorphs are characterized by the X-ray diffraction spectrapresented respectively in FIGS. 1, 2, 3, 4, 5 and 6 and are alsocharacterized by the differential thermal analysis thermograms presentedin FIGS. 7 and 8, measured using a Mettler FP 800. The X-ray diffractionpattern and the differential thermal analysis thermogram, measured usinga Mettler FP 800, of idazoxan hydrochloride (form II) are presented inFIGS. 2 and 7 respectively. As regards the differential thermalanalysis, it should be pointed out that the use of another make or ofanother model of differential thermal analysis device (for example,Perkin-Elmer) can result in a different thermogram. The presentinvention is characterized by the values of the thermogram which arepresented here and which are obtained using a Mettler FP 800 and by thevalues of an equivalent thermogram which are obtained using other typesof differential thermal analysis devices.

It is also one of the objects of the present invention to protect thesesix forms I, II, III, IV, V and VI as such.

The polymorph of form I is characterized by an X-ray diffraction patterncomprising characteristic peaks at approximately 4.0200, 6.6400, 6.9000,7.0800, 8.0800, 9.0000, 9.9600, 9.9600, 10.8400, 11.7200, 12.1400,12.3800, 12.9800, 13.3000, 13.5200, 14.9000, 15.0600, 15.2400 and21.4000 degrees θ. The polymorph of form I is also characterized by anX-ray diffraction pattern comprising characteristic peaks atapproximately 4.0200, 6.6400, 6.9000, 7.0800, 8.0800, 9.0000, 9.9600,9.9600, 10.8400, 11.7200, 12.1400, 12.3800, 12.9800, 13.3000, 13.5200,14.9000, 15.0600, 15.2400 and 21.4000 degrees θ and lacking at least onepeak at approximately 4.7400, 5.7200, 8.9200, 16.8600 or 18.9000 degreesθ. The polymorph of form I is also characterized by a differentialthermal analysis thermogram exhibiting a single maximum value atapproximately 207.5±0.2.

The polymorph of form II is characterized by an X-ray diffractionpattern comprising characteristic peaks at approximately 4.7400, 5.7200,6.6800, 7.5000, 8.9200, 9.9600, 11.5200, 12.3000, 12.9400, 13.5400,14.3000, 15.6800, 16.8600 and 18.9000 degrees θ. The polymorph of formII is also characterized by a differential thermal analysis thermogramexhibiting a single maximum value at approximately 203.9±0.4.

The polymorph of form III is characterized by an X-ray diffractionpattern comprising characteristic peaks at approximately 4.0400, 4.7000,5.7400, 6.6200, 6.9200, 7.4600, 8.0400, 8.7800, 8.9800, 9.9800, 10.8200,11.4600, 11.6400, 12.3200, 12.9400, 13.5400, 14.2400, 15.0600, 15.6200and 16.8400 degrees θ. The polymorph of form III is also characterizedby a differential thermal analysis thermogram exhibiting a singlemaximum value at approximately 203.8±0.5.

The polymorph of form IV is characterized by an x-ray diffractionpattern comprising characteristic peaks of approximately 4.8000, 5.9000,6.8400, 7.3200, 8.0800, 8.6600, 9.4600, 9.6800, 11.1600, 11.4000,11.9000, 12.2200, 12.6800, 13.8400, 14.4200, 14.9800 and 18.1000 degreesθ. The polymorph of form IV is also characterized by an X-raydiffraction pattern comprising characteristic peaks at approximately4.8000, 5.9000, 6.8400, 7.3200, 8.0800, 8.6600, 9.4600, 9.6800, 11.1600,11.4000, 11.9000, 12.2200, 12.6800, 13.8400, 14.4200, 14.9800 and18.1000 degrees θ and lacking at least one peak at approximately 6.6800,13.5400, 15.6800, 16.8600 or 18.9000 degrees θ. The polymorph of form IVis also characterized by a differential thermal analysis thermogramexhibiting a single maximum value at approximately 205.3±0.5.

The polymorph of form V is an idazoxan hydrochloride monohydrate whichis characterized by an X-ray diffraction pattern comprisingcharacteristic peaks at approximately 5.0400, 5.8400, 7.9400, 9.2800,9.4400, 10.1200, 12.0200, 12.5600, 12.9200, 13.7400, 13.9400, 14.5200,14.8200, 15.2800, 16.2800 and 16.7400 degrees θ. The polymorph of form Vis also characterized by an X-ray diffraction pattern comprisingcharacteristic peaks at approximately 5.0400, 5.8400, 7.9400, 9.2800,9.4400, 10.1200, 12.0200, 12.5600, 12.9200, 13.7400, 13.9400, 14.5200,14.8200, 15.2800, 16.2800 and 16.7400 degrees θ and lacking at least onepeak at approximately 4.7400, 6.6800, 7.5000, 8.9200, 11.5200, 14.3000,15.6800 or 18.9000 degrees θ. The idazoxan monohydrate polymorph of formV is also characterized by a differential thermal analysis thermogramexhibiting a single maximum value at approximately 205.6±0.4.

The polymorph of form VI is characterized by an X-ray diffractionpattern comprising characteristic peaks at approximately 5.6150, 6.7350,7.5350, 9.5250, 10.3450, 10.6050, 11.0350, 11.2850, 11.5350, 12.1150,12.3750, 12.9550, 13.5150, 13.9950, 14.5250, 14.9350, 15.0450, 15.1950,16.3450, 17.0450, 17.2850, 17.5750 and 17.8250 degrees θ.

The invention provides a method for the synthesis of the idazoxanpolymorph of form I and VI according to a process comprising thefollowing stages: (i) reaction of catechol and 2-chloroacrylonitrile inthe presence of pulverized potassium carbonate and of tetrabutylammoniumbromide as a catalyst, in a mixture of toluene and of dioxane, (ii)evaporation of the toluene and production of a racemic mixture of2-cyano-1,4-benzodioxane, (iii) cyclization of the2-cyano-1,4-benzodioxane in the presence of ethylenediamine and ofhydrochloric acid, (iv) addition of hydrochloric acid to crystallize andto remove the excess ethylenediamine and (v) recrystallization of theidazoxan hydrochloride from ethanol. Thus it is that the polymorph ofform I is obtained. The process for the synthesis of polymorph of formVI comprises further (vi) keeping form I in suspension in ethanol 1000under constant agitation and at room temperature during 1 to 4 days,(vii) filtration under vacuum and (viii) drying in an oven under vacuum.The process for the synthesis of polymorph of form VI may also comprisefurther after step (v) of synthesis of polymorph of form I the followingsteps: (vi′) keeping form I in suspension in ethanol 1000 under constantagitation at high temperature, (vii′) distillation of ethanol undervacuum until partial solvent evaporation to induce crystallisation,(viii′) cooling down the solution at 0° C. (ix′) filtration and dryingin an oven.

The present invention also provides a method for the synthesis of theidazoxan polymorphs of forms III and IV according to a processcomprising the following stages: (i) reaction of catechol and2-chloroacrylonitrile in the presence of pulverized potassium carbonateand of tetrabutylammonium bromide as a catalyst, in a mixture of tolueneand of dioxane, (ii) evaporation of the toluene and production of aracemic mixture of 2-cyano-1,4-benzodioxane, (iii) cyclization of the2-cyano-1,4-benzodioxane in the presence of ethylenediamine and ofhydrochloric acid, (iv) addition of hydrochloric acid to crystallize andto remove the excess ethylenediamine, (v) recrystallization of theidazoxan hydrochloride from ethanol and (vi) purification of theidazoxan hydrochloride by recrystallization either with ethanol, toobtain the form III, or with 1-butanol, to obtain the form IV. Thus itis that the polymorphs III and IV are obtained.

The present invention also provides a method for the synthesis of anidazoxan hydrochloride monohydrate, denoted in the present document asform V, according to a process comprising the following stages: (i)reaction of catechol and 2-chloroacrylonitrile in the presence ofpulverized potassium carbonate and of tetrabutylammonium bromide as acatalyst, in a mixture of toluene and of dioxane, (ii) evaporation ofthe toluene and production of a racemic mixture of2-cyano-1,4-benzodioxane, (iii) cyclization of the2-cyano-1,4-benzodioxane in the presence of ethylenediamine and ofhydrochloric acid, (iv) addition of hydrochloric acid to crystallize andto remove the excess ethylenediamine, (v) recrystallization of theidazoxan hydrochloride from ethanol and (vi) reslurrying in five volumesof a mixture of 80% of acetone and of 20% of water. Thus it is that themonohydrate is obtained. The invention also encompasses the hydrates ofidazoxan and the pharmaceutical compositions comprising such hydrates.The term “hydrate” covers, but without implied limitation, hemihydrates,monohydrates, dihydrates, trihydrates and other substances of the sametype.

The composition according to the invention is administered orally and isthus formulated in a form suitable for oral administration, preferablyin the solid form. Mention may be made, among suitable solid oralpresentations, of: tablets, hard gelatin capsules, granules and otherpresentations of the same type. The pharmaceutical compositions suitablefor oral administration comprise, in addition to the polymorphiccompounds of the present invention, or their mixtures, theirderivatives, their analogues or their pharmaceutically acceptable saltsor hydrates, a carrier, a diluent or an excipient which is alsoacceptable pharmaceutically. Any inert excipient, commonly used ascarrier or diluent, can be used in the compositions of the presentinvention, whether they are, for example, gums, starches (for example,maize starch, pregelatinized starch), sugars (for example lactose,mannitol, sucrose or dextrose), cellulose materials (for example,microcrystalline cellulose), acrylates (for example, poly(methylacrylate)), calcium carbonate, magnesium oxide, talc, or mixtures ofthese. A preferred diluent is lactose monohydrate. When they areprovided in the form of solid tablets, the compositions can additionallycomprise a disintegrating agent (for example, microcrystallinecellulose), a lubricant (for example, glyceryl behenate) and a flowagent (for example, colloidal silica).

In a preferred embodiment, the pharmaceutical composition comprisesidazoxan hydrochloride, lactose monohydrate, microcrystalline cellulose,glyceryl behenate and colloidal silica. More preferably, thepharmaceutical composition comprises 10% by weight of idazoxanhydrochloride, 61.46% by weight of lactose monohydrate, 26.34% by weightof microcrystalline cellulose, 2% by weight of glyceryl behenate and0.2% by weight of colloidal silica.

In one embodiment of the present invention, the composition isformulated in the form of tablets which preferably have a mass ofbetween 50 mg and 1000 mg, preferably between 100 and 600 mg, morepreferably approximately 100 mg, 200 mg, 300 mg, 400 mg or approximately500 mg.

The present invention also encompasses pharmaceutical compositionscomprising any solid or liquid physical form of any one of the idazoxanpolymorphs described here. For example, the idazoxan polymorphs can beprovided in a crystalline form and can have any particle size. Theparticles of the idazoxan polymorphs can be micronized or agglomeratedand can be provided in the form of particulate granules, of powders orof any other solid physical form, the preferred embodiment correspondingto a solid form.

It is particularly advantageous to formulate the oral compositions inthe unit dosage form for easier administration and a uniform dosage. Theunit dosage form as used here refers to physically discrete unitssuitable for a unit dosage for the subject to be treated; each unitcomprising a predetermined amount of active compound calculated toproduce the desired therapeutic effect in combination with the requiredpharmaceutical vector. The specifications of the unit dosage forms ofthe invention are dictated by the unique characteristics of the activecompound and by the specific therapeutic effect which has to beobtained, and by the limitations inherent in the art of the compositionof such an active compound for the treatment of individuals, thesespecifications also depending directly on the above elements.

The pharmaceutical compositions can be present in a packaging, acontainer or a distributing device at the same time as the instructionsfor use.

Advantageously, the said tablets are provided in a leaktight packagingwhich can be composed of a tablet bottle made of polypropylene or ofhigh-density polyethylene, an aluminium sachet or an “all-aluminum”blister pack.

The pharmaceutical composition according to the instant invention mayalso be in a form suitable for parenteral, intraperitoneal, intravenous,intra-arterial, transdermal, sublingual, intramuscular, rectal,transbuccal, intranasal, liposomal, vaginal or intraocularadministration or in a form suitable for local delivery by catheter orstent.

An additional aspect of the present invention is targeted at a processfor the manufacture of the said compositions by direct tableting of apowder mixture. This manufacturing process is preferred to a processinvolving a stage of granulation with a wetting liquid as, surprisingly,a conventional binder, such as povidone, is incompatible with thisactive principle. Alternatively, the direct tableting process comprisesa stage of dry granulation, for example by compacting, which precedesthe tableting stage. In the process for manufacturing by tableting, theidazoxan salt has a particle size, expressed by its mean diameter, ofbetween 50 and 250 microns, preferably of between 75 and 150 microns andmore particularly in the region of 100 to 125 microns. Furthermore, theidazoxan salt or the idazoxan hydrate has a bulk density of between 0.4and 0.8 and preferably of between 0.5 and 0.7 and more preferably stillin the region of 0.6.

The present invention also concerns a method for treating and/orpreventing a pathology selected from the group consisting of depression,Parkinson's disease and severe psychotic disorders, such asschizophrenia and schizoaffective disorders, comprising the step ofadministering to a patient in need of such a treatment a composition ora tablet according to the invention.

According to another preferred embodiment, the invention furtherconcerns a method for treating and/or preventing serious psychoticmental disorders, in particular schizophrenia and schizoaffectivedisorders, comprising the step of administering to a patient in need ofsuch treatment a tablet or a composition of the invention with a secondmedicament, preferably an atypical neuroleptic, more preferably anatypical neuroleptic exhibiting a greater antagonist affinity for thedopamine D₂ receptor than is its antagonist affinity for theα₂-adrenoreceptor. For a definition of atypical neuroleptics, see UnitedStates Patent Application 2004/0127489 and international patentapplication WO 2004/011031 based on U.S. Patent Applications U.S.60/398,718 and U.S. 60/398,719, filed on 29 Jun. 2002. Mention may bemade, among atypical neuroleptics, of olanzapine, quetiapine,risperidone, sertindole or ziprasidone. More preferably, the atypicalneuroleptic is olanzapine. The administration of the said firstmedicament and of the said second medicament is carried outsimultaneously, separately or sequentially, in any order.

Other characteristics and advantages of the invention will becomeapparent in the continuation of the description with the examplesrepresented below. In these examples, reference will be made to thefollowing figures. These figures and examples are intended to illustratethe present invention and may not under any circumstances be interpretedas being able to limit the scope thereof.

FIG. 1: X-ray diffraction diagram for the idazoxan hydrochloridepolymorph of form I;

FIG. 2: X-ray diffraction diagram for the idazoxan hydrochloridepolymorph of form II;

FIG. 3: X-ray diffraction diagram for the idazoxan hydrochloridepolymorph of form III;

FIG. 4: X-ray diffraction diagram for the idazoxan hydrochloridepolymorph of form IV;

FIG. 5: X-ray diffraction diagram for idazoxan hydrochloride monohydrateof form V;

FIG. 6: X-ray diffraction diagram for the idazoxan hydrochloridepolymorph of form VI as compared to this of form I;

FIG. 7: Differential thermal analysis thermogram for the idazoxanhydrochloride polymorph of form I, II, III and V;

FIG. 8: Differential thermal analysis thermogram for the idazoxanhydrochloride polymorph of form IV.

EXAMPLE NO. 1 Stability Study on Formulations Comprising IdazoxanHydrochloride

Idazoxan hydrochloride belongs to the category of α₂-adrenoreceptorantagonists. The chemical name of this molecule is2-(2-imidazolinyl)-1,4-benzodioxane hydrochloride and its molecularformula is C₁₁H₁₂N₂O₂HCl.

Idazoxan is provided in the form of a slightly hygroscopic, white tosubstantially white powder which is readily soluble in water andmethanol and which is soluble to fairly soluble in ethanol.

Because of its slight hygroscopicity, it has to be stored in a leaktightpackaging, with exclusion of moisture.

During all the tests carried out, this molecule exhibited the followingcharacteristics:

-   -   Idazoxan hydrochloride content of between 99.0 and 101.0%    -   Individual content of known impurities ≦0.2%    -   Individual content of unknown impurities ≦0.1%    -   Total content of impurities ≦1.0%

The main impurity of idazoxan hydrochloride is known as 791011:N-(2-aminoethyl)-1,4-benzodioxane-2-carboxamide. The stability of theactive principle was studied under various conditions of stress:

+4° C. in a closed bottle (reference)

50° C., open bottle

40° C., 30% RH, open bottle

40° C., 75% RH, open bottle

Whatever the conditions, idazoxan hydrochloride does not undergo anyorganoleptic change and no significant chemical instability is observed,even for high relative humidities (percentage of 791011≦0.03% andabsence of unknown impurities).

Compatibility studies were carried out at 40° C., 75% RH, for 1 monthbetween idazoxan hydrochloride and various conventional excipients ofthe dry forms.

The results obtained are displayed in Table 1 below and express thesurprising difference in behaviour of the binary mixtures betweenmonitoring immediately after manufacturing and monitoring after 1 monthunder stressing conditions, whereas the active principle alone isperfectly stable.

TABLE 1 Active principle/ % Excipient Excipient Ratio 791011 FunctionLactose monohydrate 1/4 0.1 Diluents Anhydrous lactose 1/4 0.3 Mannitol1/4 0.3 Sorbitol 1/4 40.8 Microcrystalline 1/2 3.7 Diluent/ celluloseBinder/ Disintegrating agent Calcium 1/2 4.4 Disintegratingcarboxymethyl- agent cellulose Povidone 4/1 8.5 Binder Hydroxypropyl-4/1 1.5 Binder methylcellulose (HPMC) Magnesium stearate 4/1 17.0Lubricant Talc 4/1 1.0 Glidant

The excipients which are most compatible with idazoxan hydrochloride arelactose, mannitol, microcrystalline cellulose and HPMC. This study showsthe high reactivity of idazoxan hydrochloride in the presence ofexcipients conventionally used in pharmaceutical formulating.

A conventional gelatin-based hard gelatin capsule form was developed inpreparing the first formulations of this molecule.

Lactose or mannitol were used as diluents because of the results of thebinary compatibilities. These diluents were used in combination withconventional lubrication excipients: talc and magnesium stearate.

These formulations were lubricated with talc and magnesium stearatedespite the negative result obtained with magnesium stearate, this beingdone in order to confirm this incompatibility at the real level of useof magnesium stearate.

The hard gelatin capsules manufactured were packaged in a leaktightpackaging (polypropylene tablet bottle) because of the slighthygroscopicity of the active principle and because of the risk of ringopening with the formation of the impurity 791011 (product itselfreactive).

The compositions of the formulations prepared are presented in Table 2below:

TABLE 2 Formu- Formu- Formu- lation lation lation Component 1 2 3Function Idazoxan 20 mg 20 mg 20 mg Active hydrochloride principleAnhydrous lactose 130.2 mg 0 0 Diluents Lactose mono- 0 0 158 mg hydrateMannitol 0 130.2 mg Microcrystalline 0 0 20 mg cellulose Magnesium 0.8mg 0.8 mg 2 mg Lubricant stearate Talc 4.0 mg 4.0 mg 0 Hard gelatincapsules, size 3

After 1 month under stable conditions in a tablet bottle at 40° C., 75%RH, the analyses show a totally unacceptable level of decompositionproduct (cf. Table 3 below):

TABLE 3 Formulation 1 Formulation 2 Formulation 3 Percentage of 3.0%2.0% 2.9% 791011

It is therefore impossible to formulate idazoxan hydrochloride in asimple hard gelatin capsule formulation; a posteriori, it has beendemonstrated that this active principle is incompatible with gelatin.

Furthermore, the formulations demonstrate the incompatibility ofmagnesium stearate.

The tablet formulation proves to be necessary in order to providesatisfactory stability of the active principle. Furthermore, analternative to magnesium stearate has been identified with glycerylbehenate.

In order to provide good homogeneity of distribution of the activeprinciple, as far as possible independently of the physicalcharacteristics of the active principle, and of the excipients, tabletmanufacture by wet granulation is studied first.

Wet granulation was carried out in a high-speed mixer/granulator withwater. The granules obtained are dried in a fluidized air bed and thengraded on a 0.4 mm screen.

Two procedures were selected:

-   -   Either granulation of all the diluent, binder/disintegrating        agent and active principle. After granulation, drying and        sieving, lubrication is carried out by mixing the particle with        the lubricant.    -   Or granulation of half the diluent and half the        binder/disintegrating agent with all the active principle. After        granulation, drying and sieving, mixing the particle with the        other half of the binder/disintegrating agent and diluent, then        addition of the lubricant last and mixing.

The tablets were subsequently packaged in all-aluminium blister packs orin leaktight tablet bottles.

The formulations employed and the pharmacotechnical results aredescribed respectively in Tables 4 and 5 below:

TABLE 4 Formu- Formu- Formu- Formu- lation lation lation lation Startingmaterial 4 5 6 7 Idazoxan 20 mg 20 mg 30 mg 30 mg hydrochloride (5%)(10%) (10%) (20%) Diluent: lactose 332 mg  156 mg  205 mg  104 mg Lubricant: glyceryl  8 mg  4 mg  5 mg  4 mg behenateBinder/disintegrating 40 mg 20 mg 60 mg 21 mg agent: micro- (10%) (10%)(20%) (15%) crystalline cellulose TOTAL 400 mg  200 mg  300 mg  140 mg 

Granulation was carried out with 10% of wetting liquid with respect tothe total mass of the tablet.

TABLE 5 Starting Formulation Formulation Formulation Formulationmaterial 4 5 6 7 % 791011 4.54% 0.44% 5.2% <0.2% Hardness 30 N 40 N 40 NNonexistent Splitting − − − +++

Additional studies carried out with a formulation qualitativelyequivalent to the formulation 5 have shown that an idazoxanhydrochloride content of 10% with respect to the total mass of thetablet, in combination with a microcrystalline cellulose content of 10%,was that which made it possible to obtain the best compromise betweenthe hardness of the tablets and the splitting during tableting.

The results obtained with regard to feasibility (hardness and splitting)are satisfactory in the range from 5 to 10% of idazoxan hydrochloride,in combination with 8% to 15% of binder/disintegrating agent ofmicrocrystalline cellulose type.

Thus, experiments have been continued until the formulation No. 5 hasbeen optimized; with this aim, two amounts of wetting liquid weretested: 5% and 20%.

Formulation 8: 5% of wetting liquid

Formulation 12: 20% of wetting liquid

The results relating to these formulations are expressed in Table 6below. The level of impurity was determined after one month at 40° C.,75% RH.

TABLE 6 Level of impurity CV Of % of wetting liquid 791011 HardnessSplitting content  5% (formulation 5a) 1.5% 20 N +++ 8% 20% (formulation5b) 2.3% 20 N − 7%

The degree of dilution studied for the active principle (10%) does notmake it possible to achieve satisfactory homogeneities in mixing(coefficient of variation in content >6%), for from 5 to 20% of waterused in wetting during the granulation.

Furthermore, the levels of decomposition obtained, although slightlylower, remain comparable with those obtained with the formulationstested in hard gelatin capsules (of between 1.5 and 2.3% of product791011).

With regard to the manufacture of tablets, the alternative process towet granulation is direct tableting. In view of the results obtained ingranulation, it is therefore logical to study the possibilities of thisprocess relating to idazoxan hydrochloride.

The pharmacotechnical characteristics of the active principle are asfollows:

-   -   Bulk density of between 0.5 g/ml and 0.8 g/ml    -   Mean diameter of between 100 and 300 μm    -   Favourable aptitude for tableting: on an alternating tablet        press, if a force of 10000 newtons is applied, the hardness of        the tablets obtained with pure active principle (volume=1 cm³)        is between 10 N and 30 N with regard to a round format with an        area of 1 cm².

The formulations employed are presented in Table 7 below:

TABLE 7 Starting Formulation Formulation Formulation Formulationmaterials 8 9 10 11 Function Idazoxan 20 mg 20 mg 20 mg 20 mg Activehydrochloride principle Lactose 158 mg 152 mg 0 122.92 mg Diluentmonohydrate Mannitol 0 0 158 mg 0 Microcrystalline 20 mg 20 mg 20 mg52.68 mg Binder/ cellulose disintegrating agent Glyceryl 0 8 mg 0 4 mgLubricant behenate Magnesium 2 mg 0 2 mg 0 Lubricant stearate Anhydrous0 0 0 0.4 mg Flow agent colloidal silica TOTAL 200 mg

The tablets obtained were packaged in leaktight blister packs(all-aluminium).

The pharmacotechnical results obtained after manufacture are describedin Table 8 below, along with the percentage of impurity found after 1month at 40° C., 75% RH.

TABLE 8 Formu- Formu- Formu- Formu- lation lation lation lation Results8 9 10 11 Hardness 20 newtons 21 newtons 25 newtons 50 newtons (formatD8R10) Splitting ++ ++ +++ + Sticking + ++ +++ + CV in  5.1%   8%  7.4% 4.1% content % Impu- 1.78% 2.41% 1.12% 1.03% rity 791011

The formulation 11 has the best hardness and exhibits the lowest levelof impurity and therefore has been selected.

The formulations 8, 9 and 10 have hardnesses which are too low for it tobe possible to envisage industrial manufacture on a rotary press.Furthermore, the splitting and the sticking observed are totallyunacceptable. This formulation 11, obtained by direct tableting, istherefore the best compromise in achieving technical feasibility of thedirect tableting form and satisfactory stability of the activeprinciple.

The stability is also satisfactory via leaktight packaging of blisterpack type, 45 μm aluminium, sealed by 20 μm aluminium (see Table 9below).

TABLE 9 Stability, 24 months, Formulation 11 Conditions: 25° C., 60%Relative Humidity 0 1 3 6 12 24 month month months months months monthsIdazoxan 19.51 19.66 20.00 19.88 18.84 19.16 hydrochloride content(mg/tablet) % of decomposition 0.24 0.66 0.74 1.06 1.19 1.64 product791011

EXAMPLE 2 Examples of Formulations

Formulation 1: Idazoxan hydrochloride 5% Microcrystalline cellulose 10%Glyceryl behenate 5% Colloidal silica 0.1% Lactose monohydrate q.s. for100%

This formulation makes it possible to manufacture tablets assayingbetween 10 mg and 30 mg of idazoxan hydrochloride packaged inall-aluminium blister packs.

Formulation 2: Idazoxan hydrochloride 5% Microcrystalline cellulose 40%Glyceryl behenate 1% Colloidal silica 0.1% Lactose monohydrate q.s. for100%

This formulation makes it possible to manufacture tablets assayingbetween 10 mg and 30 mg of idazoxan hydrochloride packaged inall-aluminium blister packs.

Formulation 3: Idazoxan hydrochloride 5% Microcrystalline cellulose 40%Glyceryl behenate 5% Colloidal silica 0.5% Lactose monohydrate q.s. for100%

This formulation makes it possible to manufacture tablets assayingbetween 10 mg and 30 mg of idazoxan hydrochloride packaged inall-aluminium blister packs.

Formulation 4: Idazoxan hydrochloride 20% Microcrystalline cellulose 10%Glyceryl behenate 5% Colloidal silica 0.1% Lactose monohydrate q.s. for100%

This formulation makes it possible to manufacture tablets assayingbetween 10 mg and 30 mg of idazoxan hydrochloride packaged inall-aluminium blister packs.

Formulation 5: Idazoxan hydrochloride 20% Microcrystalline cellulose 40%Glyceryl behenate 2% Colloidal silica 0.1% Lactose monohydrate q.s. for100%

This formulation makes it possible to manufacture tablets assayingbetween 10 mg and 30 mg of idazoxan hydrochloride packaged inall-aluminium blister packs.

Formulation 6: Idazoxan hydrochloride 20% Microcrystalline cellulose 40%Glyceryl behenate 5% Colloidal silica 0.1% Lactose monohydrate q.s. for100%

This formulation makes it possible to manufacture tablets assayingbetween 10 mg and 30 mg of idazoxan hydrochloride packaged inall-aluminium blister packs.

Formulation 7: Idazoxan hydrochloride 10% Microcrystalline cellulose26.34% Glyceryl behenate 2% Colloidal silica 0.2% Lactose monohydrateq.s. for 100%

This formulation makes it possible to manufacture tablets assayingbetween 10 mg and 30 mg of idazoxan hydrochloride packaged inall-aluminium blister packs.

N.B.: The results of the physicochemical analyses of these tablets givenas examples (Formulations 1 to 7), manufactured on an industrial rotarypress, after placing in a leaktight packaging, showed:

-   -   a disintegration time for the tablets of less than 15 minutes        immediately after manufacture and over time    -   a percentage of dissolved active principle of greater than 80%        in 30 minutes after manufacture and over time    -   CV in content values of less than 6%    -   a mean content of active principle in the tablets to ±5% of the        theoretical dosage    -   good stability over time, the sum of the impurities being less        than 2% after 24 months at 25° C., 60% RH    -   good microbiological quality after manufacture and over time

EXAMPLE 3 Stability and Decomposition Profile

A photostability study according to the ICH criteria showed nodecomposition.

Furthermore, an accelerated and long-term conditions stability study wascarried out, and the long-term stability of the polymorph of form I isshown in Table 10:

TABLE 10 Long-term stability (in months) Batch of the form I 25° C./60%RH¹ 30° C./70% RH 40° C./75% RH OP2 24 24 9 500 24 24 6 501 24 24 6 5039 6 6 504 9 6 6 ¹RH = relative humidity

EXAMPLE 4 Analysis of the Solubility of the Polymorph of Form I

The solubility of the polymorph of form I in various solvents is shownin Table 11.

TABLE 11 Batch of the form I Water Ethanol Ethyl acetate OP2 Freelysoluble Soluble Virtually insoluble 500 Freely soluble Soluble Virtuallyinsoluble 501 Freely soluble Soluble Virtually insoluble 503 Freelysoluble Soluble Virtually insoluble 504 Freely soluble Soluble Virtuallyinsoluble 507 Freely soluble Moderately Virtually soluble insoluble 508Freely soluble Soluble Virtually insoluble

EXAMPLE 5 Synthetic Processes 5.1. Processes for the Synthesis ofIdazoxan Hydrochloride of the Prior Art

Idazoxan hydrochloride can be synthesized according to the publishedmethod described below:

Preparation of 2-[2-(1,4-benzodioxanyl)]-2-imidazoline hydrochloride. Asolution of sodium methoxide (1.45 g) in methanol (20 ml) is added inthe space of one minute to a stirred solution of2-cyano-1,4-benzodioxane (145 g) in methanol (870 ml) at ambienttemperature. After stirring for a further 4 hours at ambienttemperature, the solution is cooled and ethylenediamine (64.7 g) isadded dropwise at a temperature of 5° C. A solution of hydrogen chloridein methanol (134 g of solution comprising 34.8 g of hydrogen chloride)is then added to the stirred solution in the space of 2 hours and at atemperature of 5° C. After a further 20 hours at 0-10° C., theprecipitated ethylenediamine dihydrochloride is removed by filtrationand the filtrate is reduced to 300 g under vacuum at 40° C.Ethylenediamine dihydrochloride is again removed and the remainingfiltrate is subjected to evaporation under vacuum at 40° C. to completedryness. The solid residue (225 g) is stirred with dichloromethane (1.1litres) and dry hydrogen chloride is sparged in at 5-10° C. until aslight excess is obtained. The crude product is subsequently removed byfiltration (172 g) and combined with a second crop (24 g) obtained byconcentrating the filtrate under vacuum at 40° C. The crystallization ofthese two crops from ethanol with hot filtration and concentration ofthe filtrate under vacuum until 384 g are obtained gives an off-whitecrystalline product (175.5 g, 81%), melting point 207-208° C. If theethylenediamine and the hydrogen chloride are added to the methanol inthe reverse order, a similar yield is obtained.

5.2.—Processes for the Synthesis of Idazoxan Hydrochloride withPolymorphs

Idazoxan hydrochloride comprising a polymorph of any one of the forms Ican be synthesized according to the method described below:

(a) Stage 1. The first stage consists in obtaining2-cyano-1,4-benzodioxane from the reaction of catechol and2-chloroacrylonitrile in the presence of pulverized potassium carbonateand of tetrabutylammonium bromide as a catalyst, in a mixture of tolueneand dioxane. The reaction is carried out at a temperature of between 80and 90° C. After a double decoloration, the toluene is evaporated and anoily extract of 2-cyano-1,4-benzodioxane in the racemic form isobtained.

(b) Stage 2. In the presence of sodium methoxide,2-cyano-1,4-benzodioxane gives an imidate, not isolated, which isfurther cyclized to idazoxan in the presence of ethylenediamine and ofhydrochloric acid. The excess ethylenediamine is crystallized byaddition of hydrochloric acid and then removed by filtration.Recrystallization of idazoxan hydrochloride is carried out from ethanol.The medicinal substance obtained corresponds to the racemic form I.

A stage of additional purification using different solvents makes itpossible to obtain different polymorphs of idazoxan hydrochloride.

(c) Stage 3—Purification. Purification of the final compound is possiblewhen any one of its characteristic features does not meet thespecifications.

For the impurities such as sulphated ash, heavy metals andethylenediamine content, the retreatment consists in returning to thebase form, followed by liquid/liquid washing, before returning to thehydrochloride form. A recrystallization is then carried out.

In the case of nonconformity with respect to the clarity of thesolution, the colouring of the solution, the pH of the solution, the2-chloroacrylonitrile content and the associated substances(high-pressure liquid chromatography), the retreatment consists of arecrystallization.

In the case of nonconformity with respect to the water content and theresidual solvents, drying is carried out.

This purification/recrystallization stage can be carried out using thefollowing solvents: acetonitrile, n-propanol, methanol, ethanol,1-butanol and n-butanol.

The form III is obtained by recrystallizing the form I with ethanol.

The form IV is obtained by recrystallizing the form I with 1-butanol.

An idazoxan hydrochloride monohydrate (form V) is obtained byreslurrying the form I in 5 volumes of an acetone/water mixture.

The form VI may be obtained by keeping a suspension of 1 dry weight ofform I in 7 volumes of ethanol 1000 under constant agitation and at roomtemperature during 1 to 4 days, filtrating under vacuum and drying in anoven under vacuum at 70° C. overnight.

The form VI may also be obtained by keeping a solution of form I inethanol under constant agitation and at high temperature, distillatingethanol under vacuum until partial solvent evaporation to inducecrystallisation, cooling down the solution to 0° C. over a period of 3hours, filtrating and drying in an oven under vacuum at 70° C.overnight.

EXAMPLE 6 Crystallographic Analysis by Powder X-Ray Diffraction on theIdazoxan Polymorphs I to VI

Crystallography by powder X-ray diffraction was carried out on theidazoxan forms I to VI obtained in accordance with the process of thepresent invention as described in detail in Table 12 below.

TABLE 12 Samples of idazoxan polymorphs analysed by crystallography bypowder X-ray diffraction Sample of polymorphs Process Form I Examples5.1 and 5.2 Form II Example 5.1 Form III Example 5.2 (ethanol) Form IVExample 5.2 (1-butanol) Form V Example 5.2 (water/acetone) Form VIExample 5.2

The samples were analysed using a Philips PW 1730 device equipped with ahorizontal goniometer CGR of type C and with a Cu anticathode (λ=1.54051Å), operating at 40 kV and 20 mA.

The sample was prepared according to the standard operating procedure,in accordance with the instructions of the manufacturer, using a platesample holder without spurious effects. The samples were analysed aftergentle grinding using a pestle and mortar to guarantee good homogeneity.

It was observed that the melting and the decomposition of idazoxanhydrochloride do not make possible a thermal analysis study of thepolymorphs within this temperature range. Only crystallography by X-raydiffraction can make possible the discovery of different crystallineforms.

FIG. 1 represents the x-ray diffraction diagram for the idazoxanpolymorph of form I manufactured in accordance with the process of thepresent invention (Example 5.2); FIG. 2 represents the X-ray diffractiondiagram for the idazoxan polymorph of form II manufactured according tothe prior art (Example 5.1); FIGS. 3 and 4 represent the X-raydiffraction diagram for the idazoxan polymorphs of form III and IVrespectively (Example 5.2); FIG. 5 represents the X-ray diffractiondiagram for the idazoxan polymorph of form V (Example 5.2). FIG. 6represents the X-ray diffraction diagram for the idazoxan polymorph ofform VI. The data corresponding to the X-ray diffraction diagrams arepresented in Tables 13 to 18 below:

TABLE 13 Idazoxan polymorph of form I Peak Theta (degrees) D (Å) 14.0200 10.9872 2 6.6400 6.6613 3 6.9000 6.4115 4 7.0800 6.2493 5 8.08005.4801 6 9.0000 4.9238 7 9.9600 4.4534 8 10.8400 4.0956 9 11.7200 3.791910 12.1400 3.6626 11 12.3800 3.5927 12 12.9800 3.4293 13 13.300 3.348214 13.5200 3.2947 15 14.9000 2.9956 16 15.0600 2.9645 17 15.2400 2.930318 21.4000 2.1110

TABLE 14 Idazoxan polymorph of form II Peak Theta (degrees) D (Å) 14.7400 9.3213 2 5.7200 7.7283 3 6.6800 6.6216 4 7.5000 5.9012 5 8.92004.9676 6 9.9600 4.4534 7 11.5200 3.8569 8 12.3000 3.6157 9 12.94003.4397 10 13.5400 3.2899 11 14.3000 3.1185 12 15.6800 2.8500 13 16.86002.6557 14 18.9000 2.3779

TABLE 15 Idazoxan polymorph of form III Peak Theta (degrees) D (Å) 14.0400 10.9329 2 4.7000 9.4004 3 5.7400 7.7014 4 6.6200 6.6814 5 6.92006.3930 6 7.4600 5.9326 7 8.0400 5.5072 8 8.7800 5.0462 9 8.9800 4.934710 9.9800 4.4445 11 10.8200 4.1031 12 11.4600 3.8768 13 11.6400 3.817614 12.3200 3.6099 15 12.9400 3.4397 16 13.5400 3.2899 17 14.2400 3.131318 15.0600 2.9645 19 15.6200 2.8607 20 16.8400 2.6588

TABLE 16 Idazoxan polymorph of form IV Peak Theta (degrees) D (Å) 14.8000 9.2050 2 5.9000 7.4933 3 6.8400 6.4675 4 7.3200 6.0454 5 8.08005.4801 6 8.6600 5.1156 7 9.4600 4.6864 8 9.6800 4.5809 9 11.1600 3.979610 11.4000 3.8969 11 11.9000 3.7354 12 12.2200 3.6390 13 12.6800 3.509014 13.8400 3.2200 15 14.4200 3.0930 16 14.9800 2.9799 17 18.1000 2.4793

TABLE 17 Idazoxan monohydrate of form V Peak Theta (degrees) D (Å) 15.0400 8.7677 2 5.8400 7.5700 3 7.9400 5.5761 4 9.2800 4.7765 5 9.44004.6963 6 10.1200 4.3837 7 12.0200 3.6986 8 12.5600 3.5420 9 12.92003.4449 10 13.7400 3.2430 11 13.9400 3.1973 12 14.5200 3.0722 13 14.82003.0114 14 15.2800 2.9228 15 16.2800 2.7477 16 16.7400 2.6742

TABLE 18 Idazoxan monohydrate of form VI Peak Theta (degrees) D (Å) 15.6150 7.8723 2 6.7350 6.5678 3 7.5350 5.8739 4 9.5250 4.6547 5 10.34504.2893 6 10.6050 4.1853 7 11.0350 4.0241 8 11.2850 3.9361 9 11.53503.8519 10 12.1150 3.6701 11 12.3750 3.5941 12 12.9550 3.4358 13 13.51503.2959 14 13.9950 3.1850 15 14.5250 3.0712 16 14.9350 2.9887 17 15.04502.9673 18 15.1950 2.9387 19 16.3450 2.7370 20 17.0450 2.6278 21 17.28502.5924 22 17.5750 2.5509 21 17.8250 2.5163

These results reflect the crystalline structure of the polymorphs.

The different degrees of crystallinity of the different forms examinedhave resulted in significant variation in the intensities, in particularwith the substantially modified intensity of the X-rays at 4.02 degreesθ. The diffraction diagrams of the forms II, III and IV are visiblydifferent from one another. For example, the diffraction diagram of theform II has three diffraction peaks at 5.52, 7.5 and 11.52 degrees θ.The peak at 4.04 degrees θ, characteristic of the form III, is notpresent in the diffraction diagram of the form II. The form III exhibitsa diffraction peak at 4.70 degrees θ which is not present in thediffraction diagram of the form IV. The form IV exhibits two peaks at8.78 and 8.98 degrees θ which are not present in the diffraction diagramof the form III. The diffraction diagram of the form V is also uniqueand easy to distinguish from the others.

EXAMPLE 7 Differential Thermal Analysis on the Idazoxan Polymorphs I toV

Differential thermal analysis was carried out on the idazoxan polymorphsof form I to V obtained in accordance with the process of the presentinvention (Example 5.2).

The samples were placed in closed and crimped aluminium containers.Three samples of 4 mg of each of the forms I to V were analysed. Thetemperatures for the beginning of melting were determined in accordancewith the instructions of the IUPAC by measuring the temperature at theintersection of the extended base line (linear portion of thedifferential thermal analysis curve) with the tangent of the steepestslope of the front side of the peak. The final temperatures correspondto the tip of the peaks. The equipment was calibrated using the enthalpyof fusion of indium (28.5 J/g) as reference value. The samples weresubjected to two analyses at 10° C./min from 30 to 240° C. and from 150to 240° C. The object of the second analysis was to determine withaccuracy the temperatures of the beginning and end of melting. For thispurpose, four determinations were carried out for each sample and themean of these values, as well as the relative error, were calculatedusing the Student-Fischer tables (t=3.182 for P=0.05). The enthalpieswere calculated in the same way but on the basis of five determinations(t=2.776, P=0.05).

A thermogravimetric analysis was carried out on 9.888 mg of idazoxanmonohydrate of form V from 30 to 400° C., under nitrogen, at 10° C./min.

FIGS. 6 and 7 represent representative differential thermal analysisthermograms (as measured on the abovementioned device) for the forms Ito V of idazoxan which are manufactured in accordance with the processesof the present invention.

No solid-solid transformation was observed in any sample during theincrease in temperature before melting.

The results of the multiple samples are presented in Table 19:

TABLE 19 Differential thermal analysis Temperature of the beginningTemperature peaks Polymorph (° C.) (° C.) Form I 199.3 ± 0.3 207.5 ± 0.2Form II 198.1 ± 0.5 203.9 ± 0.4 Form III 196.9 ± 0.3 203.8 ± 0.5 Form IV200.4 ± 0.3 205.3 ± 0.5 Form V   201 ± 0.4 205.6 ± 0.4 Form VI 198.9 ±1.6 208.1 ± 1.0

As shown by the data presented here, the forms I to VI of idazoxanexhibit unique differential thermal analysis thermograms.

Idazoxan monohydrate of form V exhibits an endothermic peak, indicatingthe loss of a water molecule, at 87.5±0.4° C. with an enthalpy ofdehydration of 207.6±5.6 J/g. A second endothermic peak begins at201±0.4° C. and ends at 205.6±0.4° C., which corresponds to the meltingpoint of the sample and occurs in the decomposition range of themolecule. This decomposition is displayed by an exothermic peak aftermelting situated in the vicinity of 220° C.

The endotherms of the different idazoxan polymorphs analysed can varyaccording to the speed of heating, that is to say the rate of thescanning, at which the differential thermal analysis is carried out, thecalibration standards used, the calibration of the device, the relativehumidity and the chemical purity. For any given sample, the endothermobserved can also differ from one device to another but it willgenerally remain within the ranges defined by the present document,provided that the devices are similarly calibrated.

EXAMPLE 8 8.1. Racemization of Idazoxan In Vitro

An asymmetry in the C₂ position of the idazoxan molecule gives rise totwo enantiomers, the R(−) and S(+) forms. The lability of the proton inthis position makes possible spontaneous interconversion between the twoforms. Methods coming under physiological chemistry, biochemistry andbiology were used to study the racemization of idazoxan in vitro.

The lability of the C₂ proton was studied by nuclear magnetic resonancespectroscopy so as to monitor proton-deuterium exchange in aphysiological phosphate buffer (pH 7.4) at 37° C. Approximately 50% ofthe exchange had taken place after 80 minutes and the exchange wasvirtually complete after 4 hours.

Racemization of the two enantiomers in a phosphate buffer (pH 7.4) at 25and 37° C. was studied by high-pressure liquid chromatography. Thekinetics of racemization of the two enantiomers proved to be identical,with a racemization half-life of approximately 5 hours at 25° C. and 1hour at 37° C.

The binding values of the α₂-adrenoreceptors for the two enantiomerswere evaluated using rat cortical tissue. In addition, the biologicalactivity was evaluated by the inhibition of the hypothermia induced byguanabenz in mice. Initially, the S(+) form showed a binding affinityten times greater than that of the R (−) form and proved to be 15 timesmore effective in the antagonism of the hypothermia. However,preincubation in a buffer at 37° C. for 1.5 hour for the binding testand for 4 hours in the behavioural model allowed it to be concluded thatthere was no perceptible difference in activity between the twoenantiomers, which indicates that the equilibrium of the racemizationhad indeed been achieved.

8.2. Pharmacokinetics of the Enantiomers of Idazoxan

Young healthy male subjects were allocated at random to receive a singledose of each of the following substances on one occasion: 20 mg ofidazoxan racemate (polymorph of form I); 10 mg of the R(−) enantiomer;10 mg of the S(+) enantiomer. The pharmacokinetic parameters for eachenantiomer are presented below in Tables 20 and 21.

TABLE 20 Pharmacokinetic parameters of R(−) idazoxan subsequent to asingle administration of the racemate (20 mg) or of the enantiomer alone(10 mg) Component C_(max) T_(max) AUC₀₋∞ t_(1/2) CL_(tot)/F V_(d)/Freceived (ng/ml) (hour) (ng · h/ml) (hour) (l/h) (l) Racemate 11.9 ± 4.62.1 ± 0.7 58 ± 23 3.3 ± 0.4 170 ± 76 789 ± 315 R(−) Idazoxan 10.2 ± 3.92.5 ± 0.5 43 ± 19 3.1 ± 0.6 230 ± 92 988 ± 293 S(+)Idazoxan  1.3 ± 0.73.7 ± 0.5 11 ± 6  3.7 ± 0.4 n.a. n.a. n.a.: Not applicable

TABLE 21 Pharmacokinetic parameters of S(+) idazoxan subsequent to asingle administration of the racemate (20 mg) or of the enantiomer alone(10 mg) Component C_(max) T_(max) AUC₀₋∞ t_(1/2) CL_(tot)/F V_(d)/Freceived (ng/ml) (hour) (ng · h/ml) (hour) (l/h) (l) Racemate 8.3 ± 3.62.1 ± 0.7 44 ± 21 3.3 ± 0.4 245 ± 136 1137 ± 540 R(−) Idazoxan 1.6 ± 1.04.0 ± 0   14 ± 8  4.1 ± 0.5 n.a. n.a. S(+)Idazoxan 7.2 ± 5.1 2.1 ± 0.827 ± 13 7.8 ± 0.5 397 ± 205 1515 ± 692 n.a.: Not applicable

The results indicate that the R(−) and S(+) forms of idazoxan exhibitdifferent pharmacokinetic characteristics. The S(+) enantiomer exhibitsan apparent clearance and a distribution which are approximately 1.5times better than the R(−) enantiomer but a similar t_(1/2), resultingin higher levels of R(−) in the plasma.

The two enantiomers are converted into one another according to a slowand limited process (T_(max) of approximately 4 hours; t_(1/2) forconversion of R(−) to S(+) of hours and of S(+) to R(−) of 4 hours), theformation of R(−) being slightly greater than that of S(+). Thepharmacokinetic characteristics of each enantiomer, after administrationof the racemate, combine the pharmacokinetic characteristics of theenantiomer which are determined after administration of the enantiomerin isolation, suggesting that no interaction takes place between theenantiomers when they are administered together. The concentrations ofS(+) and R(−) peak and decline at a similar rate and R(−) circulates ina greater proportion than S(+). The three medicaments administered wereall well tolerated.

EXAMPLE 9 Use of Idazoxan as Medicament for the Treatment ofSchizophrenia

Idazoxan has formed the subject of a double-blind study with a placeboas control on 17 patients suffering from schizophrenia or fromschizoaffective disorders regarded as resistant to treatment withconventional neuroleptics (R. E. Litman, W. W. Hong et al., J. Clin.Psychopharmacol., August, 13(4), 264-7 (1993); R. E. Litman, T. P. Su etal., Br. J. Psychiatry, May, 168(5), 571-9 (1996)).

The treatments of the patients were modified so as to stabilize them forat least 2 weeks with fluphenazine hydrochloride, benzotropine mesylatebeing used to control the extrapyramidal symptoms (one of the patientswas stabilized with thioridazine because of serious extrapyramidalsymptoms). Idazoxan was added at the initial dose of 20 mg twice dailyand the dose was gradually increased by 20 mg on each occasion over twoweeks up to an optimum steady dose, with a target dose of 120 mg/day,maintained for at least 4 weeks. The dosage of the idazoxan wasgradually reduced by 20 mg per day over 2 weeks, while the patients wereadministered with fluphenazine alone for at least 3 weeks. After aperiod of therapeutic withdrawal, 12 of the patients received clozapine,at an optimum dosage, for at least 5 weeks.

The addition of idazoxan to the treatment with fluphenazine led to asignificant reduction in the symptoms in comparison with a fluphenazinemonotherapy. Improvements were observed with the Bunney-Hamburg globalpsychotic assessment scale, the total score of the abbreviatedpsychiatric assessment scale, the negative symptoms of the abbreviatedpsychiatric assessment scale and the positive symptoms of theabbreviated psychiatric assessment scale, including as regards unusualthoughts and paranoiac suspicion. Even though the improvement has provedto be modest (a reduction of the order of 10 to 15% in the total scoreof the abbreviated psychiatric assessment scale), it has proved to be ofa comparable level to that obtained in the case of recourse to othernon-neuroleptic medicaments for enhancing the effect of neurolepticagents. The improvements in the total score and in the positive symptomsof the abbreviated psychiatric assessment scale correlate with themodifications observed in the plasma and urinary noradrenergicindicators. In addition, the treatment with idazoxan in combination withfluphenazine has proved to withstand comparison with that with clozapinealone.

1. A pharmaceutical composition comprising 5 to 20% of an idazoxan salt or an idazoxan hydrate, 10 to 40% of microcrystalline cellulose, 1 to 5% of lubricant, 0.1 to 0.5% of colloidal silica and 29.5% to 84.8% of lactose, with respect to the total mass.
 2. The pharmaceutical composition according to claim 1, wherein the salt is a hydrochloride.
 3. A tablet comprising the pharmaceutical composition of claim 1 or
 2. 4. A polymorphic form II of idazoxan wherein the X-Ray diffraction spectrum comprises characteristics peaks at 4.7400, 5.7200, 6.6800, 7.5000, 8.9200, 9.9600, 11.5200, 12.3000, 12.9400, 13.5400, 14.3000, 15.6800, 16.8600 and 18.9000 degrees θ; and the differential thermal analysis thermogram exhibits a single maximum value at approximately 203.0±0.4.
 5. The S(+) enantiomer of the polymorphic form II of idazoxan of claim
 4. 6. The R(−) enantiomer of the polymorphic form II of idazoxan of claim
 4. 7. The pharmaceutical composition according to claim 1 or 2, wherein said idazoxan is a polymorph of form II wherein the X-Ray diffraction spectrum comprises characteristic peaks at 4.7400, 5.7200, 6.6800, 7.5000, 8.9200, 9.9600, 11.5200, 12.3000, 12.9400, 13.5400, 14.3000, 15.6800, 16.8600 and 18.9000 degrees θ; and the differential thermal analysis thermogram of the polymorph of form II exhibits a single maximum value at approximately 203.0±0.4.
 8. A tablet comprising the pharmaceutical composition of claim
 7. 9. A polymorphic form III of idazoxan wherein the X-Ray spectra comprises characteristic peaks at 4.0400, 4.7000, 5.7400, 6.6200, 6.9200, 7.4600, 8.0400, 8.7800, 8.9800, 9.9800, 10.8200, 11.4600, 11.6400, 12.3200, 12.9400, 13.5400, 14.2400, 15.0600, 15.6200 and 16.8400 degrees θ; and the differential thermal analysis thermogram exhibits a single maximum value at approximately 203.8±0.5.
 10. The S(+) enantiomer of the polymorphic form III of idazoxan of claim
 9. 11. The R(−) enantiomer of the polymorphic form III of idazoxan of claim
 9. 12. The pharmaceutical composition according to claim 1 or 2, wherein said idazoxan is the polymorph of form III wherein the X-Ray diffraction spectrum comprises characteristic peaks at 4.0400, 4.7000, 5.7400, 6.6200, 6.9200, 7.4600, 8.0400, 8.7800, 8.9800, 9.9800, 10.8200, 11.4600, 11.6400, 12.3200, 12.9400, 13.5400, 14.2400, 15.0600, 15.6200 and 16.8400 degrees θ; and the differential thermal analysis thermogram of the polymorph of form III exhibits a single maximum value at approximately 203.8±0.5.
 13. A tablet comprising the pharmaceutical composition of claim
 12. 14. A polymorphic form IV of idazoxan wherein the X-Ray diffraction spectrum comprises characteristic peaks at 4.8000, 5.9000, 6.8400, 7.3200, 8.0800, 8.6600, 9.4600, 9.6800, 11.1600, 11.4000, 11.9000, 12.2200, 12.6800, 13.8400, 14.4200, 14.9800 and 18.1000 degrees θ; and the differential thermal analysis thermogram of said polymorph of form IV exhibits a single maximum value at approximately 205.3±0.5.
 15. The S(+) enantiomer of the polymorphic form IV of idazoxan of claim
 14. 16. The R(−) enantiomer of the polymorphic form IV of idazoxan of claim
 14. 17. The pharmaceutical composition according to claim 1 or 2, wherein said idazoxan is the polymorph of form IV wherein an X-ray diffraction spectrum comprises characteristic peaks at 4.8000, 5.9000, 6.8400, 7.3200, 8.0800, 8.6600, 9.4600, 9.6800, 11.1600, 11.4000, 11.9000, 12.2200, 12.6800, 13.8400, 14.4200, 14.9800 and 18.1000 degrees θ; and the differential thermal analysis thermogram of said polymorph of form IV exhibits a single maximum value at approximately 205.3±0.5.
 18. A tablet comprising the pharmaceutical composition of claim
 17. 19. A polymorphic form IV of idazoxan wherein the X-Ray diffraction spectrum comprises characteristic peaks at 4.8000, 5.9000, 6.8400, 7.3200, 8.0800, 8.6600, 9.4600, 9.6800, 11.1600, 11.4000, 11.9000, 12.2200, 12.6800, 13.8400, 14.4200, 14.9800 and 18.1000 degrees θ and lacking at least one peak at 6.6800, 13.5400, 15.6800, 16.8600 or 18.9000 degrees θ; and the differential thermal analysis thermogram of said polymorph of form IV exhibits a single maximum value at approximately 205.3±0.5.
 20. The S(+) enantiomer of the polymorphic form IV of idazoxan of claim
 19. 21. The R(−) enantiomer of the polymorphic form IV of idazoxan of claim
 19. 22. The pharmaceutical composition according to claim 1 or 2, wherein said idazoxan is the polymorph of form IV having an X-ray diffraction spectrum comprising characteristic peaks at 4.8000, 5.9000, 6.8400, 7.3200, 8.0800, 8.6600, 9.4600, 9.6800, 11.1600, 11.4000, 11.9000, 12.2200, 12.6800, 13.8400, 14.4200, 14.9800 and 18.1000 degrees θ and lacking at least one peak at 6.6800, 13.5400, 15.6800, 16.8600 or 18.9000 degrees θ; and the differential thermal analysis thermogram of said polymorph of form IV exhibits a single maximum value at approximately 205.3±0.5.
 23. A tablet comprising the pharmaceutical composition of claim
 22. 24. A polymorphic form V of idazoxan wherein the X-Ray diffraction spectrum comprises characteristic peaks at 5.0400, 5.8400, 7.9400, 9.2800, 9.4400, 10.1200, 12.0200, 12.5600, 12.9200, 13.7400, 13.9400, 14.5200, 14.8200, 15.2800, 16.2800 and 16.7400 degrees θ; and the differential thermal analysis thermogram of the polymorph of form V exhibits a single maximum value at approximately 205.6±0.4.
 25. The S(+) enantiomer of the polymorphic form V of idazoxan of claim
 24. 26. The R(−) enantiomer of the polymorphic form V of idazoxan of claim
 24. 27. The pharmaceutical composition according to claim 1 or 2, wherein said idazoxan monohydrate is the polymorph of form V comprising an X-ray diffraction spectrum comprising characteristic peaks at 5.0400, 5.8400, 7.9400, 9.2800, 9.4400, 10.1200, 12.0200, 12.5600, 12.9200, 13.7400, 13.9400, 14.5200, 14.8200, 15.2800, 16.2800 and 16.7400 degrees θ; and the differential thermal analysis thermogram of the polymorph of form v exhibits a single maximum value at approximately 205.6±0.4.
 28. A tablet comprising the pharmaceutical composition of claim
 27. 29. A polymorphic form V of idazoxan wherein the X-Ray diffraction spectrum comprises characteristic peaks at 5.0400, 5.8400, 7.9400, 9.2800, 9.4400, 10.1200, 12.0200, 12.5600, 12.9200, 13.7400, 13.9400, 14.5200, 14.8200, 15.2800, 16.2800 and 16.7400 degrees θ and lacking at least one peak at approximately 4.7400, 6.6800, 7.5000, 8.9200, 11.5200, 14.3000, 15.6800 or 18.9000 degrees θ; and the differential thermal analysis thermogram of the polymorph of form V exhibits a single maximum value at approximately 205.6±0.4
 30. The S(+) enantiomer of the polymorphic form V of idazoxan of claim
 29. 31. The R(−) enantiomer of the polymorphic form V of idazoxan of claim
 29. 32. The pharmaceutical composition according to claim 1 or 2, wherein said idazoxan monohydrate is the polymorph of form V characterized by an X-ray diffraction spectrum comprising characteristic peaks at 5.0400, 5.8400, 7.9400, 9.2800, 9.4400, 10.1200, 12.0200, 12.5600, 12.9200, 13.7400, 13.9400, 14.5200, 14.8200, 15.2800, 16.2800 and 16.7400 degrees θ and lacking at least one peak at approximately 4.7400, 6.6800, 7.5000, 8.9200, 11.5200, 14.3000, 15.6800 or 18.9000 degrees θ; and the differential thermal analysis thermogram of the polymorph of form V exhibits a single maximum value at approximately 205.6±0.4.
 33. A tablet comprising the pharmaceutical composition of claim
 32. 34. A polymorphic form VI of idazoxan wherein the X-Ray diffraction spectrum comprises characteristic peaks at 5.6150, 6.7350, 7.5350, 9.5250, 10.3450, 10.6050, 11.0350, 11.2850, 11.5350, 12.1150, 12.3750, 12.9550, 13.5150, 13.9950, 14.5250, 14.9350, 15.0450, 15.1950, 16.3450, 17.0450, 17.2850, 17.5750 and 17.8250 degrees θ; and the differential thermal analysis thermogram of the polymorph of form VI exhibits a single maximum value at approximately 208.1±1.0.
 35. The S(+) enantiomer of the polymorphic form VI of idazoxan of claim
 34. 36. The R(−) enantiomer of the polymorphic form VI of idazoxan of claim
 34. 37. The pharmaceutical composition according to claim 1 or 2, wherein said idazoxan is a polymorph of form VI wherein the X-Ray diffraction spectrum comprises characteristic peaks at 5.6150, 6.7350, 7.5350, 9.5250, 10.3450, 10.6050, 11.0350, 11.2850, 11.5350, 12.1150, 12.3750, 12.9550, 13.5150, 13.9950, 14.5250, 14.9350, 15.0450, 15.1950, 16.3450, 17.0450, 17.2850, 17.5750 and 17.8250 degrees θ; and the differential thermal analysis thermogram of the polymorph of form VI exhibits a single maximum value at approximately 208.1±1.0.
 38. A tablet comprising the pharmaceutical composition of claim
 37. 